Navigation system with counter circuits for pulse timing and delay



Sept. 19, 1950 J. D. wooDwARD 2,523,244

NAVIGATION SYSTEM WITH COUNTER cIRcuITs FOR PULSE TIMING AND DELAY 5 Sheets-Sheet 1 Filed June 18, 1948 Sept. 19, 1950 J, D, wooDwARD 2,523,244

NAVIGATION SYSTEM WITH COUNTER CIRCUITS FOR PULSE TIHING AND DELAY 5 Sheets-Sheet 2 Filed June 18, 1948 www Ig l

'IIIIIIIII Jaim zw/ampara ATTORNEY Jig Sept 19, 1950 J. D. wooDwARD 2,523244 NAVIGATION SYSTEM WITH COUNTER CIRCUITS FOR PULSE TINING AND .DELAY Filed June 18, 1948 5 Sheets-Sheet 3 lNvEN'roR Si .mnwfmmz if J BY ATTORNEY Sept. 19, 1950 J. D. wooDwARD 2,523,244 I NAVIGATION SYSTEM WITH COUNTER CIRCUITS FOR PULSE TIIIING AND DELAY l wlw-mdr' I www fr y L manor/envi fcwwf Y l I l/igEr/aun w INVENTOR I hnlfmdward ATTORNEY Sept, 19, 1950 J. D. wooDwARD 2,523,244

mamon sys'ma wrm couum cmcun-s Fon PULSE nume. um DELAY Filed .June 1B, 194e 5 shuts-sheet 5 WWII B /Yhraf Patented Sept. 19, 1950 NAVIGATION SYSTEM WITH COUNTER CIR- CUITS FOR PULSE TlllIING AND DELAY John D. Woodward, Sewell, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 18, 1948, Serial No. 33,846

13 Claims. (Cl. 343-103) My invention relates to radio navigation systems of the type utilizing the time difference in the propagation of radio pulses from synchronized ground stations, and to counter systems designed to produce pulses which have selected repetition rates and which are'delayed selected amounts.

Navigation systems of the above-mentioned type employ pairs of synchronized ground transmitting stations that emit radio pulses having a fixed time relation. Each pair of ground stations preferably transmits pulses at an assigned individual repetition rate for the purpose of station selection. The pulses are broadcast so that they may be received by means of equipment located in the aircraft or ships whose positions are to be determined. By means of the receiving equipment, the operator on the craft determines the time difference between the pulses from the two transmitter stations of one pair as they arrive at the receiver. Since the radio pulses travel from the ground transmitters to the receiver at a known propagation rate (i. e., at the velocity of light), it is known that the position of the craft is at some point on a line corresponding to the time difference reading. By obtaining the time difference reading from a second pair of ground stations. a second line corresponding to the second time difference reading is obtained, and the intersect point of the two lines is the position of the craft. Special maps having the time difference or loran lines printed thereon for the several pairs of ground stations are provided for use with the navigation system.

In order to measure the time difference in the arrival of successive pulses from a pair of ground stations, the receiving equipment is arranged to generate pulses at selected repetition rates. The pulses may be adjusted to have a denite'time relation to time of arrival of the ground station pulses and are provided for the purpose of driving or synchronizing cathode-ray deiiecting circuits. The deiiecting circuits produce cathoderay sweep traces on which the received ground station pulses are displayed, According to the present invention, these selected-repetition-rate and adjustably-delayed pulses are obtained from a system of counters and switching to be described in detail hereinafter.

For the purpose of selecting a particular pair of ground stations, the operator selects the particular pulse repetition rate for the driving or svnchronizing pulses corresponding to the repetition period of the pulses transmitted from said pair whereby the deecting circuits may be synchronized with the received pulses from the selected pair of ground stations. This repetition rate selection is accomplished by adjusting the repetition-rate-determining switches of a chain of counters as described hereinafter. Thus a particular pair of ground stations is selected at the receiver apparatus by setting the said counter switches to preselected positions. This preferably is done by turning a single station selection knob operating the several counter switches. Assuming the station selection switches are ganged, the station selection knob is turned to a position indicated on the receiver panel for obtaining sweep synchronizing pulses having the same repetition period as that of the pulses being transmitted from the selected pair of ground stations. Now the received pulses from the selected pair of ground stations can be made to appear stationary on the cathode-ray sweep or trace whereas those received from the other pairs of ground stations will move along the same trace.

The pulses from the two transmitter stations of a selected pair will be referred to as A and B pulses, respectively, and the B pulse is identified in the present system as the pulse that occurs after or follows the mid-point of the other pulse period. In operation, the A and B pulses are displayed, respectively, first on two slowsweep cathode-ray traces and then on two fastsweep cathode-ray traces, thereby enabling the operator to obtain an alignment of the A and B pulses by adjusting another set of switches of said chain of counters, referred to as delay-determining switches, so that the time vdifference between the pulses driving or synchronizing the cathode-ray deecting circuits equals exactly the time difference between A and B pulses.

It will be noted that the chain of counters has two sets of switches connected to it, one for determining the repetition rate and the other for determining the amount a pulse is delayed. The action of each is independent of the action of the other. 4

The adjustment for the display and alignment of the A andB pulses is accomplished by first setting the A pulse at the left end of the upperslow-sweep trace, when the receiving apparatus is switched to an operating position marked #1. The B pulse will then appear on the lower cathode-ray trace and a variable index marker may now be located under the B pulse, this being done by adjusting the several delay switches to delay the variable index marker the correct amount. The apparatus is then switched to a #2 fastsweep operation position so that the A and B- exact adjustment of the delay switches, the adjustable fast-sweep wave is caused to start at the proper time to bring the A and B pulses into alignment. In order to insure exact alignment, the A and B pulses should be made to have the same amplitude, and an amplitude balance control circuit is provided for this purpose. After these adjustments have been made, the time difference between the starts of the fast sweeps will exactly equal the time diierence between the A and B pulses from the transmitters, and this time difference can be read directly from the settings of the delay switches.

The counter chain and switching system described in this application is not limited to use in a. navigation system but, rather, is of general application where adjustably-delayed signals are desired and, especially, where it is also desired to select diierent repetition rates for the signals.

In the specific example herein described as applied to a, navigation system, the counter chain comprises four decade counters that divide by followed by a frequency divider. that divides by 4. 'I'he first stage of the divide by 4 unit is a binary counter (a multivibrator) that is the last stage, strictly speaking, of the counter chain. The second multivibrator of the divide by 4 unit has no reset pulse applied to it. The decade counters are preferably of the general type described in application Serial No. 580,446, now Patent No. 2,521,788, issued September 12, 1950, filed March 1, 1945 in the name of Igor E. Grosdoff. More specifically, the counter and switching combination utilizes principles described in application Serial No, 719,035 filed December 28, 1946 in the name of Charles J. Young, now Patent 2,490,500 issued December 6, 1949, but includes improvements over and additions to the combination disclosed by Young. As to the counter and switching system per se, a feature of novelty in the present invention is the combining of two sets of switches with the counter chain so that one set of switches determines repetition rate while the other set of switches determines delay. The way in which this is accomplished will be described in detail hereinafter.

An object of the present invention is to provide an improved method of and means for determining the time difference between electrical pulses.

A further object of the invention is to provide improved receiving equipment for a radio navigation system of the type utilizing the propagation of radio pulses from pairs of synchronized ground stations. l

A still further object of the invention is to provide an improved method of and means for indicating the time difference between radio pulses transmitted from synchronized ground stations.

A still further object of the invention is to provide an improved method of and means for obtaining a direct reading of the time difference between radio pulses transmitted from synchronized ground stations.

A still further object of the invention is to provide an improved means for obtaining signals that are delayed selected amounts.

A still further object of the invention is to provide an improved method of and means for obtaining signals of selected repetition rates that are delayed selected amounts.

A still further object of the invention is to provide an improved method of and means for producing pulses that recur at selected repetition rates and that may be adjusted in timing or phase.

'I'he invention will be better understood from the following description taken in connection with the accompanying drawing in which:

Figure 1 is a block and circuit diagram of navigation receiving apparatus designed in accordance with one embodiment of the invention,

Figures 2 and 3, to be placed side by side, are block and circuit diagrams of the counter and the associated repetition rate switching and delay switching shown in block in Figure 1,

Figure 4 is a block diagram representing one pair of ground radio transmitter stations of the navigation system which transmit A and B pulses, respectively, y

Figure 5 is a group of graphs which are referred to in explaining the operation of the navigation system shown in Figure 1,

Figure 6 is a group of graphs which are referred to in explaining the operation of the counter system shown in Figures 1, 2 and 3.

Figure 7 is a view of the slow-sweep cathoderay traces appearing on the screen end of the cathode-ray indicator tube that is included in the apparatus of Figure land of the received pulses A and B as they appear on the traces when they are aligned,

Figure 8 is a View of the fast-sweep cathoderay traces on the cathode-ray tube indicator and of the received pulses A and B as they appear on the two fast-sweep traces, respectively, during the next step in obtaining more exact alignment of the A and B pulses,

Figure 9 is a view showing the fast-sweep traces of Figure 8 superimposed or collapsed for the final alignment step and showing the A and B pulses exactly aligned and superimposed, and

Figures 10 and 11 are circuit diagrams of the horizontal deflecting slow-sweep and fast-sweep circuits, respectively, employed in the system of Figure 1.

In the several figures, similar parts are indicated by similar reference characters.

THE COUNTER CHAIN AND ASSOCIATED REPETITION RATE SWITCHES AND DELAY SWITCHES Referring to the navigation receiving apparatus shown in Figures 1, 2 and 3, the pulse-producing system comprises a crystal oscillator I0 that produces a sine wave voltage of stable frequency which in the example illustrated is l megacycle per second, the repetition period being 1 microsecond. The frequency of the crystal oscillator output may be increased or de-l creased slightly by a manual adjustment as indicated at the control knob Il for obtaining a right or left drift of a received pulse on a cathode-ray sweep trace.

The crystal oscillator I 0 drives a decade counter I2 to produce periodic pulses which recur at the rate of kilocycles per second. The repetition period or time interval between Successive pulses is, therefore, 10 microseconds.

The frequency of the 10/is. pulses is divided by ten by means of a second decade counter I3 to produce 100 ps. pulses. The frequency of the 100 as. pulses is divided by 10 by means of a third decade'counter I4 to produce 1000 ,us. pulses. The frequency of the 1000 us. pulses is divided by 10 by means of a fourth decade counter I6 to produce 10,000 as. pulses, and the frequency of these is divided by 4 by means of a frequency divider or counter I1 to produce 40,000 es. pulses. As explained hereinafter, the decades and the rst stage of the divider I1 comprise a counter chain. The output of divider I1 is in the form of a square wave having the repetition period of 40,000 as. This square wave is always symmetrical regardless of the repetition rate since the reset pulses are not applied to the second and last stage of the divider I1 as will be understood from the later detailed description. The square output wave is passed through a cathode follower tube I8 and from it are obtained a vertical separation wave and, by means of a shaping circuit, a. pulse for driving or synchronizing the fixed horizontal fast-sweep deflection as explained hereinafter.

A variable index marker pulse, which is obtained from a gate circuit No. 2, is adjustable in timing or delay whereby it may be .shifted along the sweep trace when a slow sweep is 'used and whereby it may be utilized to trigger the adjustable fast sweep when the fast sweep is used.

The amount the variable index marker pulse is delayed is determined by the setting of time delay switches SID, S2D, S3D, S4D, and SSD. These switches, as shown in Figure 3, are multipole, multi-contact switches that are connected to the several anodes of the multivibrator tubes in the counters. This is an important feature of the invention and will be described in detail hereinafter in connection with Figures 2 and 3.

The repetition rate of the pulse from gate No. 2, as well as that of the other pulses taken off the counter chain, including the pulse taken off a gate circuit No. 1, may be varied for the purpose of station selection by means of repetition rate switches SIR, S2R, S3R, S4R, and S5R which are similar to the delay switches SID, etc. and which are connected to the anodes of the counter tubes in a similar fashion. Pulses taken off the switches SIR, etc. are passed through the gate circuit No. 1 and are supplied to a pulse generator 49 which may comprise a Thyratron as explained hereinafter.

The pulse output of gate No. 1 is also applied to each of the counters for resetting them as indicated in Figure 1 and as will be explained in the more detailed description with reference to Figures 2 and 3.

A detailed description of Figures 2 and 3 will be given later, but rst the other parts of the navigation system will be explained. In the example being described, it will be assumed that the rst pair of ground stations transmit the A pulses with a repetition period of 40,000 as. and transmit the B pulses with a like repetition period; that the second pair of ground stationstransmit A and B pulses having a repetition period of 39,900 as.; that the third pair transmits 39,800 as. pulses; that the fourth pair transmits 39,700 "ps, pulses, etc. It is apparent that for station selection at the receiving apparatus, the operator must be able to select corresponding repetition periods for the output pulses of the counter system which control the cathode-ray deflection cycle; namely, periods of 40,000 as.; 39,900 as.; 39,800 as.; 39,700 as.; 39,600 ps.; etc.

However, it may be preferred to employ a different group of repetition periods than the group of 40,000 as., 39,900 as., etc. assumed above. For example, repetition periods of 30,000 as., 29,900 as., etc. may be employed. Or, as another example, repetition periods of 50,000 gs., 49,900 ps., etc. may be employed.

CA'rHoDE RAY TRACE PRESENTATION At this point, it may be well to give a description of the operation of the receiving apparatus In Figure 5, the graphs X and W show the wav shapes of the slow-sweep and fast-sweep horizontal deecting Waves, respectively, for obtaining the desired cathode-ray traces. vThefwave .'V comprises a pair of recurring pulses, the second ofwhich (referred yto as the variable index marker) is adjustable in time and determines the starting time t of the wave f-g of the graph W.` l

The starting time t of the variable index marker in relation to the xed index marker maybe adjusted by adjusting the switches SID, S2D, etc'. (Figures 1 and 3), as wil1 be explained herein-- after, for aligning the A and B pulses. Three switching positions identified as positions #1, #2 and #3 are used successively in aligning the A and B pulses. It will be .understood that while the pulses A and B and their corresponding fastsweep traces appear alternately on the cathoderay tube screen, they appear to the eye to occur simultaneously `because of persistence of vision, lag of phosphorescence of the screen or both.

vAs shown in Figure 5, the B pulse is the one that Aoccurs after the mid-point of the A pulse period, and consequently the time interval, which elapses between the occurrence of a-B pulse and the succeeding A pulse will be less than one-half pulse interval. As will be seen in Figure 5, the start of one fast sweep (h-i) coincides with the start of a slow trace, while the start of the other fast sweep (f-y) coincides with the variable index marker.

As already explained, a momentary change of the recurrence rate will change the location of the pulses on the trace by drifting them along the trace. Specifically, it is possible for the yoperator to locate the 'A pulse at the left side of the upper slow trace, which in turn will cause the B pulse to fall on the lower tracel and the variable index marker may be made to coincide with the B pulse. Therefore, when the function switch is turned to position #2, the A pulse will occur during the trace described by the fixed fast-sweep deflecting wave h-i, while the Bpulse will occur during the trace described by the variable fast-sweep deflecting wave ,f-g.

A finer adjustment will permit the operator to align the A and B pulses so that the time elapsed between the start of the respective fast sweeps` and the corresponding pulses are equal and occurs during the expanded parts of the traces, thereby providing good accuracy for determining the time delay. l

In the present system, after vthe A and B pulses have been aligned with the receiver switched successively to operating positions #1, #2 and #3, the desired time difference or time interval is read off the delay switches SID, 'S2D,`

SSD, SlD, and SSD (Figures 1 and 3) which indicate, respectively, microseconds in units,`. tens,

hundreds, thousands and multiples of ten thouf GENERAL DsscRIPrIoN or CA'rx-Ionr: RAY Tiuicr: PRODUCING Cm'cmrs Referring vto Figure 1 and to the graphs of Figure 5, the output of the pulse generator 49 is supplied over a conductor Sla to a slow-sweep deflecting circuit |I5 for producing a sawtooth voltage wave X.

The output of the divider |1 is a rectangular voltage wave which appears unchanged at the output of a cathode-follower tube I8 as the Wave C.

To produce the fast-sweep wave h-i of deilecting wave W (Figure 5), the wave C is supplied over a conductor |98 to a dierentiating circuit |05 to produce a pulse |05A. The pulse |05A is also utilized as the fixed index marker of the wave V.

The circuit for producing the variable index marker of wave V comprises the counter chain and associated delay switching, the said marker being obtained from the adjustably delayed pulse U taken from the gate No. 2. It is the Wave U that controls the timing of the adjustable fastsweep portion f-g of wave W.

The delayed pulse U is supplied over a conductor ||9 to the mixer |06. The mixed waves U and |05A pass through a clipper |2| and appear as the wave V which drives the fast-sweep deiiecting circuit |22 to produce the wave W.

When the system is in the No. 1 operating position, the xed and adjustable index marker pulses of the wave V are applied to the vertical deflecting plate 368 of the indicator tube |39 through a lead 383, a switch 350, a resistor 384, and a lead 38|.

Description of mixer 106, etc.

Referring to Figures 1 and 11, the mixer circuit |08 and the clipping circuit |2| function to clip off the negative pulses of the wave |05A and to mix the remaining clipped positive pulses with the pulses U. Thus, the wave V is obtained at the output of the clipper-mixer combination. The mixer |06, which may consist of two vacuum tubes having a common anode resistor as shown in Figure ll, reverses the polarity of the pulses. The waves in the plate circuit of the mixer |08 are of equal amplitude due to operation o1 the tubes in a condition where grid and plate voltage approach equal amplitude. The width of the applied pulses U and |05A is short compared to that of the plate pulses, the widthV of the latter being controlled by a capacitor-resistor combination in the plate circuit and therefore being independent of the width of the incoming wave. This capacitor-resistor combination comprises a capacitor CI and the plate resistor RI.

The wave V is supplied to the fast-sweep deilecting circuit |22 shown in detail in Figure 11 and described hereinafter. The narrow negative pulses of wave V produce the fast-sweep wave W having the useful deecting portions h-i and f-g. The dei-lecting waves W and X are applied from the circuits |22 and 5 through a wave-selecting switch |23 and through a horizontal deflecting amplifier |24 to the horizontal defiecting plates |38 of the cathode-ray indicator tube |39. As described in copending application Serial No. 589,320, now Patent No. 2,445,361, issued July 20, 1948, led April 20, 1945, in the names of Garrard Mountjoy, George D. Hulst, Jr. and Earl Schoenfeld and entitled Radio Navigation System, the horizontal delecting ampli- 11er |24 may be provided with a switch (not Cil shown) for changing the bias on the amplifier tubes when the function switch is` changed from the slow-sweep position to the fast-sweep position and `vice versa, thereby insuring optimum eiliciency and undistorted gain from the ampliner tubes.

The switch |23 has three contactpoints and three "corresponding switch positions, referred to as operating positions, which are identified,v reading clockwise, as positions #1, #2, and #3.

"(Ihere, are four other operation position switches, described hereinafter, that likewise have these three switch positions and which are ganged with the switch |23.

Switch |23, when in operation position #1, functions to apply the slow-sweep wave X to the horizontal deiiecting plates |38 and. when in operationpositions #2 and #3, functions `to apply the fast-sweep wave W to the deflecting plates |38. v

The fast-sweep deecting circuit |22 that is driven by the wave V (comprising the fixed and Variable marker pulses) to produce the fastsweep wave W will now be described with reference to Figure 11.

The fast-sweep circuit Referring more specifically to the circuit |22 for producing the fast-sweep wave W, as shown in Figure 11, the circuit comprises a vacuum tube 3|6 and a pulse-shaping network that comprises two sections consisting of cathode resistors 33| and 332 shunted by capacitors 333 and 334, respectively, identified as network sections 3|1a and 3|'|b. The shaping network further comprises a. delay line section 3|1c comprising series resistors 336 and `shunt capacitors 331 connected across the cathode resistor 33| and terminated in a resistor 338 and in the cathode resistor 332. The fast-sweep wave W is taken off the resistor 338 through an adjustable tap 339, the setting of which determines the amplitude of the wave W.

In operation, the capacitors of the network sections 3|1a and 3|1b are charged through the anode resistor 34| and the tube 3|6 to a certain voltage level between successive pulses of the wave V- to bring the tap 339 to the voltage ei. Upon theoccurrenceofeach negative pulse of the wave V, the tube 3|6 is driven to cut-oft and the capacitors 333 and 334discharge through the resistors 33| and 332, respectively. The section 3|'Ia comprising capacitor 333 and resistor 33| has a fast time constant whereby the discharge of` capacitor 333 produces a. voltage of steep slope across resistor 33|. The section 3|1a comprising capacitor 334 and resistor 332 has a slower time constant whereby lthe discharge of capa'c-4 itor 334 produces a voltage of less slope across These two voltages of different.

resistor 332. slopes appear at the tap 339 as the sum of the two voltages with the voltage of the steeper slope slightly delayed by the delay network section 3|1c. v, v

The Wave form of the wave Wg-following the said slight delay is approximately logarithmic.

It should beunderstood that the fast-sweep wave W need not beof the wave form described and, in-fact, may be linear.

The above-described fast-sweep deecting circuit is described and claimed in application Serial No. 583,255, now Patent No. 2,463,969, issued March 8, 1949, led March 17, 1945 in the name of George D. Hulst, Jr., and entitled Cathode Ray DeilectionY Circuit.

As .previously noted, the starting time t of the fast-sweep wave f--g is determined by the adi justment of the pulse U (and in turn by the variable index marker of wave V) whereby the start of the wave f-g may be made to precede the received B pulse by the same amount that the start of the wave h--i precedes the received A pulse, this being the condition of augment of the A and B pulses. It should also be noted that the wave f-g is identical with the wave IIA-i whereby exact alignment of the A and B pulses on the cathode-ray traces is obtained (as shown in Figure 9) when the above-described timing relation exists. l

An improved fast-sweep circuit described and claimed in copending application Serial No. 674,-

184, now Patent No. 2,449,169, issued Septem ber 14, 1948, filed June 4, 1946 in the names of Paul F. J. Holst and Loren R. Kirkwood and entitled Delecting Circuits,may be employed if desired.

The slow-sweep circuit Referring more specifically to the slow-sweep deflecting circuit H5, as shown in Figure 10, it comprises a vacuum tube 3|8 and a network in the cathode circuit that com-prises a cathode resistor 342 that has an adjustable tap 344 thereon and which is shunted by a capacitor 345. Positive bias is applied to the cathode of the tube 3|8 by connecting the lower end of cathode resistor 342 to the junction point of a pair of bleeder resistors 3|9 and 320. This prevents the tube 3|8 from drawing current at the end of the sawtooth cy-cle so that flattening of the sawtooth wave is avoided. The operation is as follows: Each time one of the positive 20,000 as. pulses from the lead 6|a is supplied to the grid of the tube 3|8 by way of a coupling capacitor 32|, the capacitor 343 is charged suddenly from the anode voltage supply through the tube 3|8 to a certain voltage level to bring the tap 344 to the voltage level e2 (Figure 5). At the end of each positive pulse, the capacitor 343 discharges slowly through the resistors 342 and 3 I 9 thus producing successively the slow-sweep sawtooth wave portion a-b and the sawtooth wavel portion c-d at the tap 344.

In Figures and 11, the values of certain circuit elements have been indicated, merely by way of example, in ohms, megohmsLmicrofarads and micro-microfarads.

THE RADIO RECEIVER The A and B pulses from a. pair of ground stations (Figure 4) are received by a radio receiver of the superheterodyne type comprising a radio frequency amplifier indicated at 36|, a converter 362, and I.F. ampliiier 363 and a second detector and video frequency amplifier 364. The A and B pulses are supplied with positive polarity over a conductor 366, a conductor 38| and a capacitor 382 to the upper vertical deflecting plate 368. Thus, the A and B pulses may be made to appear, as shown in Figures 7, 8 and 9, on the horizontal cathode-ray traces. The A and B pulses are made to appear with equal amplitude on the cathode-ray tube screen by employing a differential gain control circuit described hereinafter.

SLOW-SWEEP AND FAST-SWEETz TRACE SEPARATION The slow-sweep traces -b and c-d are separated as illustrated in Figure '1 while the receiver is on the #1 operation position by means of the rectangular wave C (Figure 5) supplied from the cathode follower tube 18 (Figure 1) of blanking pulses.

\ l0 over a conductor 363 to the #1 contact point of a trace separation switch 31|, and over a conductor 312 tothe upper deilecting plate 368 of the cathode-ray tube |39. Thus, the portion of the wave C, which is positive as it appears on the upper plate 368, holds the cathode-ray deection up a certain -amount during the occurrence of the slow-sweep deiiecting wave c-d. n

The fast-sweep traces f--g and hf-i are separated as illustrated in Figure 8 during the #2 l operation position also by means of the rectangular wave C.

FAST-SWEEP BLANKING f Blanking is provided so that only the traces f-g and h-- appear on the cathode-ray screen when in the #2 and`#3 fast-sweep operating p0- sitions. This blanking is provided by`means of the negative portions of the Wave Y as it appears on the anode of the tube 3|6 (Figure 11) of the fast-sweep deecting circuit |22. The wave Y is supplied from the anode of tube 3|6 to the #2 and #3 contact points of a switch 32| whereby in the labi-2 and #3 operation positions, this wave is supplied over conductors 322 and 326 to the grid'321 of the cathode-ray tube |39.

TRACE BRILLIANCE CoN'rRoI.

The diode 324 is provided to control the brilliance of the traces on the cathode-ray tube screen by preventing changes in bias on the cathode-ray tube grid 321 due to the application A leak resistor 328 is connected across the diode 324 and the cathode of the diode 324 is connected to a variable bias voltage source (not shown).

In operation, during the periods that the blanking waves are positive at the anode of the diode 324, the impedance of the diode 324 isv very low so that its anode is practically at the bias potential of its cathode. Thus, regardless of the form of the blanking wave and regardless of whether anyl blanking wave is being applied, the voltage on the grid 321 of the cathode-ray tube during the cathode-ray sweeps is substantially the voltage on the cathode of the diode 324.

DIFFERENTIAL GAIN CONTROL CIRCUIT A differential gain control circuit for the R.F. amplifier 36| of the radio receiver preferably is provided, as shown in Figure 1, for the purpose of keeping the amplitudes of the A and B pulses substantially alike at the receiver output, thus facilitating the A and B pulse alignment. The

gain control circuit includes a resistor 343 connected between Athe anodes of the two tubes of the last multivibrator in the final divider |1 (Figures 1 and 2). An adjustable differential gain balance tap on resistor 343 may be moved to either side of the center thereof to decrease the gain of the R.F. amplifier 36| during either the reception of the pulse A or the pulse B. The voltage at the gain balance tap is supplied through a lead 340, a capacitor 344 and a resistor 346 to the anode of a diode 341 and to the #2 and #3 contact points of a differential gain control switch 348. Thus, when the receiver is on either the #2 or #3 operation position for pulse alignment on the fast sweeps, the diiferential gain control voltage is applied through the switch 348 and a conductor 349 to the gain control grid of an ampliiier tube in the R.F. amplifier 36|.

The diiferential gain control operation with the receiver on either #2 or #3 operation position is as follows:

When the gain balance tap is at the center of 11 resistor 343, no voltage wave is applied to the diode 341. When the tap is on one side of this center or balance position, a waye of one polarity is applied to the diode 341; when the tap is on the other side of the balance point, a wave of the opposite polarity is applied to the diode 341.

The diode 341 functions to supply a negative bias during the negative half-cycle following .a positive cycle of an applied wave. For example, a positive half-cycle causes diode current to charge capacitor 344, and during the following negative half-cycle, the capacitor 344 discharges slowly through a resistor 35| connected across the diode 341 thus making the anode of diode 341 negative with respect to ground and reducing the gain of the R.F. amplifier 36| rWhile the B pulse (or the A pulse) is being amplifed.

With switch 348 on the #1 operation position for pulse alignment, normal operating bias voltage -V is on the R.F. amplifier 36|.

DETAILED DESCRIPTION or COUNTER CHAIN AND SWITCHING or FIGURES 2 AND 3 A more detailed description will now be given describing the system of counters, switches and gates for obtaining pulses of the desired repetition rate and of the desired delay. The specic system shown in Figures 2 and 3 provides eight different repetition rates of 40,000 ps.; 39,900 ps.; 39,800 ps., etc. for selecting any one of eight pairs of stations according to the settings of switches SIR, SZR, etc. As to the pulse delay, this particular systems delays a pulse from ps. to over 19,000 ys., according to the settings of switches SID, SZD, etc. i

Referring to Figures 2 and 3, the chain of counters, the repetition rate switching, the delay switching, and the gating or coincidence circuits are shown in detail by way of example. Decade counter No. 1 consists of multi-vibrator-like locking stages comprising double triodes VI, V2, V3 and V4. These stages each have two positions of rest at one or the other of which they stay locked, when tripped thereto, until some applied voltage or current trips them again to lock them in the other position. In the embodiment shown, application of negative voltage to the anodes and thence to the grids of the locking circuit tubes will reduce current in that tube drawing current and start the tripping action which switches the current through the other tube. Decade counters No. 2, No. 3 and No. 4 are similar and to simplify the diagram have been illustrated :by rectangles. The frequency divider or counter No. 5 is illustrated in detail and comprises `only two multivibrators MI and M2 since it divides by 4. The multivibrators in this counter are similar to those employed in the decade counters. However, the rst stage MI is the nal stage of the counterl chain. The second stage M2 has no reset pulse applied to it and it does not supply any pulse to the coincidence tube of the repetition rate system as will be apparent from the following description.

The repetition rate switching Associated with each decade counter is a threepole, ten-position switch (Figure 3) for determining the pulse repetition rate. These switches The switches SIR, S2R, S3R, S4R, and SSR. and the contacts thereof are coupled to the anodes of the locking circuit tubes whereat the potentials rise and fall depending on which tube of the pair is drawing current. For example, the anode VIA of the left-hand or A section of the tube VI is connected to alternate contacts of pole PI of the three-pole switch SIR. The anode `VIB of the right-hand or B section of tube VI is connected to the remaining contacts of this pole. The anodes V2A, V2B, and V3B of tubes V2 and V3 are connected to staggered pairs of contacts of the second pole P2, etc. The basic details of each decade and how it operates is covered fully in Grosdoft' application Serial No. 580,446, now Patent No. 2,521,788, referred to above and consequently, no detailed explanation will be given here. Associated with the binary MI vof counter No. 5 is the lsingle-pole two-position switch SER that functions with switches SIR, SZR, etc. for determining the repetition rate. Although not so illustrated, the ve switches SIR, SZR, etc. preferably are ganged so as to be operated by a single station selection knob.

The basic purpose of the counter circuit is to produce output pulses after the counters have counted a predetermined number of master oscillator cycles or pulses. v The start of the counting is controlled by a gate circuit No. l (Figure 1) and comprising tubes 26, 21, 28, 29, 30, and 34 (Figure 3) as will be explained later. The development ofthe counter chain output pulses that are to be produced after the predetermined count has been reached is obtained by combining the proper voltages from the anodes of certain tubes in all ilve counters. For example, to select station LI the repetition period of the last multivibrator M2 of counter No. 5 is made 39,900 microseconds. Since the first stage MI of counter No. 5 is the nal one in the counter chain to be reset, as explained hereinafter, the desired result is obtained by making the repetition period of its output wave D (Figure 5) one half the said period of 39,900 ps. or 19,950 as. Therefore the switch SIR on counter No. 1 is set at position 0 which is the units count, the switch SZR on counter No. 2is set on position 5 which is the tens count, switch S3R on counter No. 3 is set on position 9 which is the hundreds count, switch S4R on counter No. 4 is set on position 9 which is the thousands count, and switch SER on counter No. 5 is set on position l which is the ten thousands count.

The voltage pulses collected by the switches are comfbined by means of ve vacuum triodes 26, 21, 28, 29, and 30. The tubes are in conventional circuits including grid leak resistances BR connecting the switches to ground. Each triode is Ibiased by means of a voltage drop across a by-passed cathode resistor. This combination of pulses is obtained by the connections of said switches to the control grids of these ve tubes. The anodes of the tubes are connected together to produce a single pulse, which represents the sum of the collected pulses, and feeds the same by way of resistors 36, 31, 38, 39 and 4| and common resistor 42a to the grid 33 of a nal combining or coincidence tube 34. The tube 34 is connected in an amplifier stage with its grid grounded by a resistor 45 and its cathode grounded by a resistor 46 and its anode connected to the plus terminal of a direct current source. The anode of amplifier tube 34 is coupled by a capacitor 41 to the control grid 48 of an output tube 13 49, the purpose of which is to deliver the combined or output pulse to all of the tubes in all of the decade counters and to the tubes in the binary counter MI to trip the same back to their starting position for successive operation of the counter chain and also to deliver a pulse of the desired repetition rate to the slow sweep generator by way of the lead Gla, A negative bias voltage is applied to the grid 48 of tube 49 through a resistor 45a.

Referring to decade counter No. 1 which has its switch Sl R set at position 0, it is noted that for each position of the switch, a different combination of voltages from the eight tubes of the counter are used as explained in'the Grosdoff lf application Serial No. 580,446, now Patent No.- 2,521,788. The voltage on the switch SIR as applied to the grid of tube 26 reaches a certain maximum positive value only when the count is at the value for which the switch position is set and the nal desired output pulse applied to the grid of tube 34 is obtained only when the proper combination of voltages occurs simultaneously on the selected tubes of all five counters. For example, in decade counter No. 1 on the count of 0, the voltages selected by switch SIR are those at the anodes of tubes VIA and V2A and V4A. This combination of three voltage raises the control grid of tube 26 above its cut-off :point so that conduction is initiated in tube 26 and the potential on its anode and at resistor 36 falls. The procedure for selecting voltages by the switches will be understood by referring to the graphs of Figure 6. 1

The several graphs of Figure 6 show the voltages appearing at the several anodes of the tubes VI, V2, etc. The graph identified as VIA shows the voltage on the anode of the left-hand or A section of tube VIA, for example. The dissymmetrical characteristic of the graphs for the tubes V2 and V3 results from the feed back employed to obtain a decade count as explained in Grosdoi application Serial No. 580,446, now Patent No. 2,521,788. The dots indicate the plates that are selected to obtain a given count. For example, 4 the anodes VIA, V2A, and V4A are connected to switch points 0 to obtain the count 0 when 'the switch is set on said points 0. A similar action takes place in tubes 21, 29, 29 and 30 when the proper voltages are obtained by the settings on switches S2R, SSR, S4R., and S5R. When the final pulse which represents the final combina- 14' this tube off luntil the time occurs when tubes 26, 21', 28, 29 and'illl are simultaneously conductive, this point being when the counter chain has reached the predetermined count for which it is adjusted. '1 1 l At the instant when the counter chain produces its output pulse at the plate of tube 34, this output pulse is applied to the pulse generator tube 49 which preferably'is a vapor tube such as a Thyratron so that a large current output is obtained at the output terminal 5I of the load resistor 46a. Preferably, the tube 49 dis'- charges a capacitor 49a which receives a charge lfrom the B+ source through a resistor 49h.

Thus a high energy output pulse is produced. From terminal 5I the pulse is applied by way of lcondenser 52 and lead 42 to reset the counters of the counter chain back tothe zero or starting position. This resetting function is accomplished 1 by application of the output pulse, which is positive in polarity, to the grid circuits of all the tubes in the counters which draw current in the starting position. As previously stated, the reset pulse is not applied tothe multivibrator M2 of the frequency divider I1.

The reason for not applying a reset pulse to the multivibrator M2 is that it must supply a symmetrical square wave (wave C inFigure 5) just as in the case of the Eccles-Jordan oscillator shown in Minneman application Serial No.I 744,239, now Patent No. 2,515,464, issued July 18, 1950, led April 26, 1947. Furthermore, there is no necessity for applying a reset pulse to this last multivibrator for changing the repetition period. This will be understood from the follow-y ing.

If the desired repetition period of the Wave C (Figure 5) from the last multivibrator M2 is to be 39,900 as., it is only necessary to make the repetition period of the Wave D (Figure 5) from the preceding multivibrator MI 19,950 as. since the last multivibrator divides by 2. This, of course, is accomplished by the resetting action described. Similarly, for any other repetition period, the switches SIR, S2R, etc. are set to give the desired repetition period for the output wave D of the rst multivibrator MI of counter No. 5, which repetition period is one-half that of the output wave C. For the particular example assumed, the different switch settings for selecting eight different pairs of stations L0, LI, L2 etc. may be charted as follows:

Repetition rate switching tion of voltages from the tubes 26, 21, 28, 29, and 30 is reached, the voltage applied to the control grid of tube 34 is reduced (negative) to such a :point that conduction in the tube 34 is cut-ofi. This action occurs suddenly at the instant the counters of the counter chain reach the number or count for which the switches have been set. Also the tubes 26, 21, 28, and 29 may be made conductive several times during the process of the count, yet the combined voltage applied to the grid of tube 34 is never suicently negative to cut 7:.

The delay switching The delay switches SID, S2D, SSD, S4D, and SSD are similar to the switches illustratedfor determining the repetition period and they are connected to the chain of counters in the same way. The voltages taken off the delay switches are supplied to vacuum tubes 56, 51, 58, 59, and G9 which comprise the gate circuit No. 2 (Figure l). These tubes and their associated circuits correspond to the tubes 26, 21, 28, 29, and and their associated circuits previously described. v

The coincidence tube 6I (to which the outputs of tubes 56 to 60 are applied) and the Thyratron tube 62 correspond to the tubes 34 and 49, re-v spectively, of the repetition rate switching circuit. The delayed pulses appear on the lead I I9.

The setting of the switch SID determines the microsecond delay in units, that of switch S2D determines the delay in tens, and the settings of switches S3D, S4D, and SSD determine the delay in hundreds, thousands, and tens of thousands, respectively. For example, if the delay switches SID, S2D, S3D, S4D, and S5D are on positions 8. 5, 7, 6, and 0, respectively, as illustrated, when pulse alignment on the cathoderay tube screen is obtained, then the reading is 6758 microseconds. 'I'his reading locates one of the navigation or loran lines of position on the map prepared for use with the equipment. For convenience in setting the delay switches SID, etc., their ganged switch arms preferably are operated by rotatable knobs ID, 2D. etc. which carry pointers that indicate the delay setting.

It will be noted that since the last counter stage supplying pulses to the gate tube 60 is the binary MI, the coincidence tube 6I would supply output pulses of a repetition period of 20,000 jrs.

or less, depending on the selected repetition period, in the absence of some further circuit action. Double this repetition period is desired, of course, for driving the fast-sweep circuit to obtain the adjustable fast trace f-g (Figure 5). The desired repetition period is obtained by, in effect, blanking out alternate pulses as indicated in Figure 5 so that only the 40,000 as. repetition period pulse U appears on the lead I I9.

This blanking eiect is obtained by applying to the grid of gate tube 60 by way of a lead 'I0 a square wave from the last multivibrator M2. This wave is the same as wave C (Figure 5) extaken oi the opposite side of M2 from the side supplying the wave C. Thus, the grid of tube is held negative during the master period" (see Figure 5) whereby the pulse from the binary MI cannot pass through tube 60 during said period.

The amount a pulse is delayed is not affected by changes in the pulse repetition rate because the amount of delay is less than the shortest repetition period. In the present example, the maximum delay desired from the point of measurement (mid-point d, Figure 5) is less than 19,650 ps. which is the shortest repetition period of the wave D. The resetting action is the only thing that `would affect the delay and this does not occur until the counters have operated for more than the desired period of delay without any loss of count due to resetting.

The delay switch settings obviously do not affect the repetition rate since they do not aiect the resetting circuit.

It will be apparent that the system of counters, switches, gate tubes, and coincidence tubes described herein for obtaining pulses of selected repetition rates and selected delays is of general application and is not limited to its use in navigation apparatus. For general application it probably would be desired to omit the lead 10 so from the time of occurrence vof any reset pulse. not just from the reset pulse occurring at the mid-point d as inthe navigation system application.

From the foregoing description, it will be understood that I have provided an improved navigation apparatus of great a-ccuracy that determines time intervals or differences that are easily read by an operator; and that I have also provided a system of counters and switching of Ageneral application which supplies pulses that may be adjusted to any one of a wide range of repetition periods, with the pulses of a selected repetition period delayed with great precision any desired amount over a wide operating range.

PROCEDURE 1N MAKING A TIME MEASUREMENT The successive steps in making a measurement of the time interval between the A and B pulses from a pair of ground stations will nowy be described.

Alignment of A and B pulses POSITION #l After a particular pair of ground stations has been selected with the receiver set on the #l operation position, the A and B pulses will appear stationary on the two traces a-b and c-d. A suitable drift switch such as knob I I of oscillator I0 is operated to drift one of the pulses onto the upper trace c-d and over the fixed index marker at the left end of this trace. The other .pulse will now appear on the lower trace a-b. The pulse on the trace c-d is the A pulse and the pulse on the trace a-b is the B pulse. `That this is true will be evident by referring to the graphs of Figure 5.

Next, the starting time t of the variable index marker of wave V is adjusted by setting the delay switches SID, S2D, etc. to bring the variable index marker under the B pulse. The variable index marker is now carefully adjusted so that its position with respect to the B pulse is substantially the same as the position of the fixed index marker with respect to the A pulse.

10 SITION ji' 2 Next, referring to Figure 8, the receiver is switched to the fast-sweep operation position #2 which results in the A and B pulses. appearing on the traces .h-i and f-g, respectively. As shown in Figure 5, the start of the variable index marker pulse of wave V determines the start of the second fast-sweep portion f-g of wave W, the two starting practically simultaneously. By operating suitable drift switches such as the knob II of the crystal oscillator IIJ, the A and B pulses are drifted to the left ends of the traces where they are on the more expanded portion of the fast sweeps. They are then closely aligned as shown in Figure 8 by operating one or more of the delay switches SID, S2D, etc.

POSITION #s The final alignment of the A and B pulses is done on operation position #3 with the two traces f-g and h-i superimposed as shown in Figure 9. The front edges of the A and B pulses are now exactly aligned, usually by operating only the switch SID. The time reading can now be made from the settings of the delay switches as shown by the positions of the pointers on the switch operating knobs ID, 2D, 3D, 4D, and 5D.

For example, if the pointers of the switch knobs ID, 2D, 3D, 4D, and 5D read 8, 5, 7, 6, and 0, respectively the reading is 6758 microseconds.

17 I claim as my invention: 1. Apparatus for determining the time interval between two time-spaced pulses,.said apparatus including a pulse coincidence indicator, means comprising a chain of counters for producing an adjustably-delayed pulse, means for applying said delayed pulse to said coincidence indicator for bringing said two time-spaced pulses into coincidence, means comprising count-selecting means connected to said chain of counters for determining the amount of delay of said adiustably-delayed pulse, and means for indicating said time interval as a function of the adjustments of said count-selecting means.

2. A navigation system receiver for receiving two time-spaced pulses that are transmitted in a predetermined time relation from two geographically-spaced stations, respectively, said receiver including a pulse coincidence indicator, means comprising a chain of counters for producing an adjustably-delayed pulse, means for applying said delayed pulse to said coincidence indicator for bringing said two time-spaced pulses into coincidence, means comprising count-selecting means connected to said chain of counters for determining the amount of delay of said adjustably-delayed pulse, and means for indicating a time difference, corresponding to a navigation line of position, as a function of the adjustments of said count-selecting means when coincidence of said time-spaced pulse is obtained at said indicator.

3. A navigation system receiver for receiving two time-spaced pulses that are transmitted in a predetermined time relation from two geographically-spaced stations, respectively, said receiver including means for finding the time difference between said two pulses at the receiver, said last means comprising a chain of counters that produces an output pulse, means comprising count-selecting means connected to each of said counters for determining the repetition rate of said output pulse, and additional means comprising additional count-selecting means connected to each of said counters for determining the delay of said output pulse.

4. A navigation system receiver for receiving two time-spaced pulses that are transmitted in a predetermined time relation from two geographically-spaced stations, respectively, said receiver including means comprising a `chainv of counters that produces an output pulse, means comprising count-selecting means connected to each of said counters for determing the repetition rate of said output pulse, and additional means comprising additional count-selecting means connected to each of said counters for determining the delay of said output pulse, a cathode-ray tube having a screen, means for causing said two pulses to appear on said screen during successive cathode-ray deiiections, respectively, and means for controlling by said output pulse the starting time of alternate deflections to obtain alignmentof said two time-spaced pulses whereby the time difference between said two time-spaced pulses may be read off the settings of said additional count-selecting means after said alignment has been obtained.

5. A navigation system receiver for determining the time interval between two time-spaced pulses which recur at a certain repetition rate, said receiver including a cathode-ray tube having a screen on which said pulses are to appear and having means for causing said two pulses to appear on two traces on said screen whereby said pulses may be aligned, means for controlling the repetition rate of said traces and. for adjustably controlling the time at which alternate traces start, said last means comprising a counter chain and repetition rate switching means and time delay switching means associated therewith for producing successive pulses of said certain repetition rate with alternate pulses having a selected delay. means for starting each alternate trace in response to the occurrence of each delayed pulse, whereby said selected delay may be made such as to align said two pulseson said screen and whereby the amount of delay required for said alignment may be read oil.' said time delay switches.

` 6. In a system for determining the time inter-q val between two time-spaced pulses which recur at a certain repetition rate. said system including a cathode-ray tube having a screen on which said pulses are to appear and having means for producing a cathode ray and directing it against said screen, a deflecting circuit for producing successive similar detlecting waves, means for deflecting said cathode ray successively by said deecting waves and means for causing said timespaced pulses to produce an indication on said screen during said deections, means for controlling the repetition rate of said deecting waves and for controlling the time at which alternate defiecting waves start whereby said time-spaced pulses may be aligned on said screen, said last means comprising a counter chain and repetition rate switching means and time delay switching means associated therewith for producing a pulse of said selected repetition rate and having a selected delay. said last pulse being applied to said deilecting circuit to produce a trace on the screen during one of said timespaced pulses whereby said selected delaymay be made such as to align said two pulses on said screen.

'7. In a system for determining the time interval between two time-spaced pulses which recur at a certain repetition rate, said system including a cathode-ray tube having a screen on which said pulses are to appear and-having means for producing a cathode ray and directing it against said screen, a deilecting circuit for producing successive similar` defiecting waves, means for deiiecting said cathode ray successively by said deecting waves and means for causingr said time-spaced pulses to produce an indication on said screen during said deections, means for controlling the repetition rate of said deflecting waves 'and for controlling the time at which alternate deilecting waves start whereby said time-spaced pulses may be aligned on said screen, said last means comprising a counter chain and repetition rate switching means and time delay switching means associated therewith for producing successive pulses of said selected repetition rate with alternate pulses having a selected delay. said successive pulsesbeing applied to said deflecting circuit to produce traces on the screen during each of said time-spaced pulses whereby said selected delay may be made such as to align said two pulses on said screen.

8. In combination, a chain of counters, means comprising count-selecting means connected to each of said counters for obtaining o'utput pulses 19 counter chain, and additional means comprising additional count-selecting means connected to each of said counters for obtaining other output pulses of said repetition rate and for determining the delay of said other output pulses with respect to the start of said cycle.

9. In combination, a chain of counters, a stable oscillator connected to supply signal continuously to the high frequency end of said chain of counters, means comprising count-selecting means connected to each of said counters for obtaining output pulses and for determining the repetition rate of said output pulses, said repetition rate determining means also including means for resetting said counters by said output pulses and at the same time restarting the cycle of operation of the counter chain, and additional means comprising additional count-selecting means connected to each of said counters ior obtaining other output pulses of said repetition rate and for determining the delay of said other output pulses with respect to the start of said cycle.

10. A system for producing repetitive pulses having a selected delay with reference to a point of measurement, said system comprising a. chain of counters, each counter having a count-selecting means,a coincidence tube or circuit, means applying said selected counts from the counters of said chain to said coincidence tube whereby it passes an output pulse only in response to the selected counts from each counter occurring simultaneously, means for resetting said counters by said output pulse and at the same time restarting the cycle of operation oi.' the counter chain whereby the repetition rate of said output pulse is determined by the count selection at each of the counters; each counter of said chain having an additional count-selecting means, a second coincidence tube or circuit, means applying the counts selected by said additional countselecting means to said second coincidence tube whereby it passes an output pulse only in response to all the selected counts from each counter applied thereto occurring simultaneously and whereby said second output pulse has a delay with respect to the start of said cycle of operation determined by the count selection of said additional count-selecting means.

11. A system for producing pulses having selected repetition rates and selected delays, said system comprising a chain of counters, each counter having a count-selecting means, a coincidence tube or circuit, said selected counts from the counters of said chain being applied to said coincidence tube whereby it passes an output pulse only in response to the selected counts from each counter occurring simultaneously, means for resetting said counters by said output pulse andat the same time restarting the cycle of operation of the counter chain whereby the repetition rate of said output pulse is determined by the count selection at each of the counters; each counter of said chain having an additional count-selecting means, a second coincidence tube or circuit, the counts selected by said additional count-selecting means being applied to said second coincidence tube whereby it passes an output pulse only in response to the selected counts from each counter applied thereto occurring simultaneously and whereby said second output pulse has a delay determined by the count selection of said additional count-selecting means and a repetition rate determined by the count selection of said rst count-selecting means.

12. In combination, a stable oscillator for supplying signal at a comparatively high frequency, a chain oi' counters, means for supplying said signal to the high frequency end of said chain of counters, each counter having a count-selecting means, a coincidence tube or circuit, said selected counts from the counters of said chain being applied to said coincidence tube whereby it passes an output pulse only in response to the selected counts from each counter occurring simultaneously, mean for resetting said counters by said output pulse and at the same time restarting the cycle of operation of the counter chain whereby the repetition rate of said output pulse is determined by the count selection at each of the counters; each counter of said chain having an additional count-selecting means, a second coincidence tube or circuit, the counts selected by said additional count-selecting means being applied to said second coincidence tube whereby it passes an output pulse only in response to the selected counts from each counter applied thereto occuring simultaneously and whereby said second output pulse has a delay determined by the count selection of said additional count-selecting means and a repetition rate determined by the count selection of said first count-selecting means.

13. In combination, a chain of counters, each counter comprising a plurality of multivibrators connected in cascade, each counter having switching means connected to its multivibrators for selecting a desired count, a coincidence tube or circuit to which the selected counts from the counters are applied, said coincidence tube passing a signal only in response to all the counts applied thereto occurring simultaneously, means for applying the output pulse of said coincidence tube to said multivibrators to reset the counters and start the cycle of oper-ation again whereby the repetition rate oi said output pulse is determined by the switch selection of the counts of the counters in said chain; each counter having additional switching means connected to its multivibrators for selecting a desired count, a coincidence tube or circuit to which the counts selected by said additional switching means are applied, said last coincidence tube passing a signal only in response to al1 the counts applied thereto occurring simultaneously, and means for applying the output pulse of said last coincidence tube to a utilization circuit, said last output pulse having a repetition rate determined bythe switch selection of the counts applied to the ilrst coincidence tube and having a delay with respect to the start of the cycle of operation determined by the switch selection of the counts applied to the second coincidence tube.

JOHN D. WOODWARD.

REFERENCES CITED The following references are of record in the i'lle of this patent:

UNITED STATES PATENTS Number Name Date 2,430,570 Hulst Nov. 11, 1947 2,432,158 Hulst et al Dec, 9, 1947 2,442,692 Holst et al June 1, 1948 2,445,361 Mountjoy et a1 July 20, 1948 OTHER REFERENCES Publication Electronics for Dec. 1945, pages to 115. (CopyinDiv. 48.) 

